This invention relates to fire-resistant valves, and more particularly to metal-to-metal backseats for providing a fire-resistant seal between the stem and the bonnet of a gate valve.
As reflected in patents and other literature, much effort has been expended in recent years to provide industry, and especially that involved in oil and gas production, with stem operated valves that will withstand the destructive effects of fire or other high temperatures without losing their function of safe, fluid-tight control of high pressure systems. This effort has resulted in a variety of designs for valves with metal-to-metal seals, stem backseating, and fusible elements to prevent backseating during normal operating temperatures yet facilitate backseating when such temperatures are exceeded. The requirements for fire-resistant wellhead valves have become very stringent, including zero leakage at low operating pressure, a very difficult result to achieve especially with respect to the stem-to-bonnet backseat. In addition, the backseat seal must not be susceptible to leakage because of modest misalignment of the stem-to-backseat seal, modest interference tolerances, material cost/selection/availability, or design reliability.